Rolled metal strip, after its manufacture, will always have non-uniform or wavy edges which have to be trimmed before the strip is rolled into coils. Conventional edge trimmers utilize rotating circular knives to trim the edges of the strip in order to obtain an accurate and constant strip width. The trimmer knives may either be driven or free running. Normally, the knives, one arranged above the strip and the other below the strip, are set with predetermined horizontal and vertical clearances and they may be set parallel to the direction of advance of the strip past the knives or they may be set at a slight angle in order to achieve the optimum cutting action which is free from burrs. However, once the knives have been correctly set to trim a given thickness and width of strip, they are maintained in that position.
Apart from having wavy edges, the whole strip may be badly shaped, i.e. it may not be straight and may be curved. Such faults often give rise to tracking problems and as the strip moves over a series of rolls in the processing or trimming line it can wander from side to side. It has been proposed therefore, to guide the strip accurately to the trimmer knives, otherwise sideways movement of the strip will cause one edge of the strip to run out of contact with the knives. This can cause disastrous results because invariably the knives will not re-engage the edge of the strip again. In order to guide the strip for known trimmer knives, several steering and guiding rolls have always been provided which are expensive both because they constitute extra equipment and take up valuable space, and it is an object of this invention to overcome these disadvantages.
In an alternative prior art proposal, instead of guiding the strip to the knives, the knives are moved axially relative to the line of advance of the strip (see, for example, U.K. Pat. No. 1,335,477). This is not satisfactory with metal strips because the lateral forces bearing on the edges of the knives would be very large and the cutting edge of the knives would be damaged and possibly the knives themselves would break. In any event, it would certainly cause rapid wear which would call for replacement of the knives at frequent intervals.
The present invention has been evolved to overcome the above problems in a relatively cheap and convenient manner.